Electric Field Decay Without Pair Production: Lattice, Bosonization and Novel Worldline Instantons

Abstract

Electric fields can spontaneously decay via the Schwinger effect, the nucleation of a charged particle-anti particle pair separated by a critical distance $d$. What happens if the available distance is smaller than $d$? Previous work on this question has produced contradictory results. Here, we study the quantum evolution of electric fields when the field points in a compact direction with circumference $L<d$ using the massive Schwinger model, quantum electrodynamics in one space dimension with massive charged fermions. We uncover a new and previously unknown set of instantons that result in novel physics that disagrees with all previous estimates. In parameter regimes where the field value can be well-defined in the quantum theory, generic initial fields $E$ are in fact stable and do not decay, while initial values that are quantized in half-integer units of the charge $E=(k/2)g$ with $k\in \mathbb{Z}$ oscillate in time from $+(k/2)g$ to $-(k/2)g$, with exponentially small probability of ever taking any other value. We verify our results with four distinct techniques: numerically by measuring the decay directly in Lorentzian time on the lattice, numerically using the spectrum of the Hamiltonian, numerically and semi-analytically using the bosonized description of the Schwinger model, and analytically via our instanton estimate.

Comments: 45+22 pages, 21 figures and 7 tables; v2: typos corrected, references added; v3: matches the version published in JHEP